Atypical Spindle Cell/Pleomorphic Lipomatous Tumor

**Semantic type:** Neoplastic Process

**Definition:** A benign adipocytic neoplasm, characterized by ill-defined tumor margins and the presence of variable proportions of mild to moderately atypical spindle cells, adipocytes, lipoblasts, pleomorphic cells, multinucleated giant cells, and a myxoid or collagenous extracellular matrix. It has a low tendency for local recurrence if incompletely excised. Unlike conventional atypical lipomatous tumors, there is no risk for dedifferentiation. (WHO 2020)

**Synonyms:** - Atypical Spindle Cell Lipoma - Fibrosarcoma-Like Lipomatous Neoplasm - Spindle Cell Liposarcoma